conservatives are absolutely convinced that secretly, everyone views outgroups as filthy rats, like they do. there's a kernel of truth in that a lot more people think that way than will admit it, but conservatives usually aren't referring to that as an observed tendency. they're referring to a universal law they've made up, that anyone who claims to hold liberal or leftist democratic values is lying

apologies for overexplaining something you already know. point is I doubt they even considered whether it would actually get people to go to SF. they just wanted to fantasize about Liberals MELTING DOWN upon hearing about the sign (because of course libs secretly think people in El Paso are like rats)